Have wind farms been overestimated?

It looks like even the people who don’t think much of wind power might have been overestimating it. Not only are those gigantic wind farms unsightly, and impractical in many area…, but according to an article at Phys.org, they don’t work as well as advertised, for a reason that seems retrospectively obvious:

“People have often thought there’s no upper bound for wind power—that it’s one of the most scalable power sources,” says Harvard applied physicist David Keith. After all, gusts and breezes don’t seem likely to “run out” on a global scale in the way oil wells might run dry.

Yet the latest research in mesoscale atmospheric modeling, published today in the journal Environmental Research Letters, suggests that the generating capacity of large-scale wind farms has been overestimated. Each wind turbine creates behind it a “wind shadow” in which the air has been slowed down by drag on the turbine’s blades. The ideal wind farm strikes a balance, packing as many turbines onto the land as possible, while also spacing them enough to reduce the impact of these wind shadows. But as wind farms grow larger, they start to interact, and the regional-scale wind patterns matter more.

In other words, wind turbines interfere with each other, and the more of them you gather into a single crowded installation, the more pronounced the effect becomes. This was always factored into the calculations of wind-farm engineers, but apparently they underestimated the effect… by quite a bit.

Keith’s research has shown that the generating capacity of very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter. Previous estimates, which ignored the turbines’ slowing effect on the wind, had put that figure at between 2 and 7 watts per square meter. In short, we may not have access to as much wind power as scientists thought.

Keith is all in favor of alternative energy sources, but he sounds dubious about the possibility of wind power reaching the terawatt capacity needed to make it a viable part of a comprehensive alt-energy solution. He even went so far as to model a plan that would cover most of the planet with wind turbines… at which point they would actually begin affecting global wind patterns. The theoretical scalability of the technology – the Earth generates plenty of wind – crashes into practical limitations that have not been sufficiently explored.

“It’s clear the theoretical upper limit to wind power is huge, if you don’t care about the impacts of covering the whole world with wind turbines,” says Keith. “What’s not clear—and this is a topic for future research—is what the practical limit to wind power would be if you consider all of the real-world constraints. You’d have to assume that wind turbines need to be located relatively close to where people actually live and where there’s a fairly constant wind supply, and that they have to deal with environmental constraints. You can’t just put them everywhere.”

“The real punch line,” he adds, “is that if you can’t get much more than half a watt out, and you accept that you can’t put them everywhere, then you may start to reach a limit that matters.”

But there are no practical limits to ideology and cronyism, at least none that a physicist can measure.

I’ve always been in favor of rationally exploiting the energy resources that work – a plan currently at war with powerful special interests and radical “green” ideology – while science takes the decades it needs to perfect something better, a process I’m confident will reach a satisfactory conclusion, if we give it enough time. And we unquestionably have the reliable resources we need to buy that time.

There’s interesting news this week about a new battery technology that efficiently converts the energy of motion into stored electric power – in other words, you’d be able to charge your cell phone with the energy generated by simply walking around. The technology is in its infancy now, but its inventors have high hopes. It sounds close to what an engineer told me years ago he saw as the true evolution of alternative energy, which he thought would take the better part of a century. Imagine that sort of technology leading to cars that charge themselves through forward motion… or dare we dream of tapping into the power of planetary rotation and tectonic activity? Now that would really be something. And it wouldn’t blot out the landscape or kill birds.